The basic RNA components of the Kirsten and Harvey murine sarcoma virus genomes have been identified as (1) type-C leukemia virus RNA sequences recombined with (2) specific rat cellular RNA sequences. We have found that removal of oxygen from normal, uninfected rat cells triggers a massive induction of these same RNA sequences. We have tentatively identified a gene product of the specific rat cell sequences and have characterized an enzyme activity associated with it. We intend to confirm by in vitro translation that this gene product is also encoded by the Kirsten sarcoma virus genome. Studies will be performed aimed at defining the mechanism whereby anaerobiosis induces normal cells to express the sarcoma virus genome components. Both positive and negative control factors will be examined.